Such ejector devices are disclosed in EP 063 891 B1 or in U.S. Pat. No. 5,489,207. These ejectors are used by the dentist, for example in order to fill a patient's dental cavities with viscous plastics as tooth filling material. For that purpose a cartridge containing the tooth filling material is placed in the insertion opening of the ejector device. When pressure is exerted on the lever, the piston is driven forward into the cartridge and drives the material out of the outlet tip of the cartridge. At times great pressure is needed in order to eject the material. If the cartridge is not correctly positioned, this force might destroy the cartridge or prevent it from remaining securely in its insertion opening. The cartridge might even be forced out of the insertion opening.
It is also known from U.S. Pat. No. 4,472,141, for example, to secure cartridges in the ejector devices or fasten the outlet tip with retaining nuts. This requires great material strength at the threads in order to prevent the threads from being torn out.
The present invention is addressed to the problem of improving an ejector device such that the cartridge will be securely held without requiring the dentist to perform additional manual operations after inserting the cartridge into the ejector device.